The added radiation from mammograms and other types of tests with chest radiation might be especially harmful.

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Some studies have suggested women with the genetic mutations could be more sensitive to radiation. If those genes are damaged by radiation, they may not be able to repair DNA properly, raising the cancer risk.

Updated at 12:19 AM EDT on Friday, Sep 7, 2012

Mammograms aimed at finding breast cancer might actually raise the chances of developing it in young women whose genes put them at higher risk for the disease, a study by leading European cancer agencies suggests.

The added radiation from mammograms and other types of tests with chest radiation might be especially harmful to them and an MRI is probably a safer method of screening women under 30 who are at high risk because of gene mutations, the authors conclude.

The study can't prove a link between the radiation and breast cancer, but is one of the biggest ever to look at the issue. The research was published Thursday in the journal BMJ.

"This will raise questions and caution flags about how we treat women with (gene) mutations," said Dr. Len Lichtenfeld, deputy chief medical officer of the American Cancer Society. He and the society had no role in the research.

Mammograms are most often used in women over 40, unless they are at high risk, like carrying a mutation of the BRCA1 or BRCA2 gene. Having such a mutation increases the risk of developing cancer five-fold. About one in 400 women has the gene abnormalities, which are more common in Eastern European Jewish populations. Unlike mammograms, an MRI, or magnetic resonance imaging scan, does not involve radiation.

The breast cancer screening tests have been proven to save lives and are clearly beneficial for women aged 50 and over who have an average risk of breast cancer. Experts are divided about their value in women younger than 50.

Some studies have suggested women with the genetic mutations could be more sensitive to radiation because the genes are involved in fixing DNA problems. If those genes are damaged by radiation, they may not be able to repair DNA properly, raising the cancer risk.

In several European countries including Britain, the Netherlands and Spain, doctors already advise women with BRCA mutations to get MRIs instead of mammograms before age 30. In the U.S., there is no specific advice from a leading task force of government advisers, but the American Cancer Society recommends yearly mammograms and MRIs from age 30 for women with BRCA gene mutations.

In the BMJ study, European researchers followed nearly 2,000 women over 18 with one of the gene mutations in Britain, France and the Netherlands. Participants reported their previous chest X-rays and mammograms, including the age of their first screening and the number of procedures. About 850 women were later diagnosed with breast cancer. Roughly half of them had X-rays while one third had at least one mammogram, at an average age of 29.

The researchers did not have a breakdown of how many women were exposed to chest radiation before age 30 but estimated that for every 100 women aged 30 with a gene mutation, nine will develop breast cancer by age 40. They projected the number of cases would increase by five if all of them had one mammogram before age 30. But they cautioned their results should be interpreted with caution because most women didn't have a mammogram before 30.

Researchers found women with a history of chest radiation in their 20s had a 43 percent increased relative risk of breast cancer compared to women who had no chest radiation at that age. Any exposure before age 20 seemed to raise the risk by 62 percent. Radiation after age 30 did not seem to affect breast cancer risk.

"We believe countries who use mammograms in women under 30 should reconsider their guidelines," said Anouk Pijpe of the Netherlands Cancer Institute, one of the study authors. "It may be possible to reduce the risk of breast cancer in (high-risk) women by using MRIs, so we believe physicians and patients should consider that."

The study was paid for by European cancer groups.

Lichtenfeld said the study wouldn't immediately change advice from the American Cancer Society but said concerned women should talk to their doctor about their options. "It's not possible today to make a blanket statement about what women (with the gene mutations) should do, but physicians and patients need to weigh the risks and benefits carefully," he said.

He also warned that women who need scans involving radiation shouldn't avoid them because of breast cancer fears.

"No one should think that they should never get an X-ray because they have the BRCA1 or 2 gene mutations," he said. "Just be careful that the X-rays you get are really the ones that you need."